1. Field of the Invention
The present invention relates to a transmission line that transmits a plurality of high-frequency signals therethrough, and an electronic device including the transmission line.
2. Description of the Related Art
Various transmission lines for transmitting high-frequency signals therethrough have been proposed so far. For example, Japanese Patent No. 4962660 discloses a transmission line with a stripline structure. The transmission line disclosed in Japanese Patent No. 4962660 includes an elongated multilayer insulating body extending in a transmission direction of the high-frequency signals, a signal line, a first ground conductor, and a second ground conductor. The signal line is located inside the multilayer insulating body. The first ground conductor and the second ground conductor are arranged in a state sandwiching the signal line in a thickness direction of the multilayer insulating body (i.e., in a lamination direction of insulator layers). Furthermore, the first ground conductor and the second ground conductor are connected to each other through a plurality of via hole conductors (interlayer connecting conductors) that are arrayed along the signal line. Thus, the transmission line of the stripline structure sandwiching the signal line between the first ground conductor and the second ground conductor is provided.
In trying to arrange a plurality of transmission lines of the structure disclosed in Japanese Patent No. 4962660 close to each other in, e.g., a communication device, a plurality of signal lines may be arrayed inside one multilayer insulating body in one example. In such an example, it is conceivable to arrange the signal lines with a spacing held between the adjacent signal lines in a direction (width direction of the multilayer insulating body) that is orthogonal to both the thickness direction of the multilayer insulating body and the signal transmission direction.
In other words, when the transmission lines of the structure disclosed in Japanese Patent No. 4962660 are arrayed in the width direction of the multilayer insulating body and the multilayer insulating body is formed into an integral unit with the interlayer connecting conductor arranged between the adjacent signal lines, unwanted coupling between the adjacent signal lines is suppressed with the presence of the interlayer connecting conductor.
The above-described configuration of arranging the interlayer connecting conductors between the adjacent signal lines has the following problems.
(1) When the pitch of the interlayer connecting conductors arranged between the adjacent signal lines is set to a large value, or when the interlayer connecting conductors are omitted, unwanted coupling between the signal lines is more apt to occur. On the other hand, when the pitch of the interlayer connecting conductors is set to a small value, a capacitance generated between the signal line and the interlayer connecting conductor is increased, and the desired characteristic impedance as the transmission line is hard to realize.
(2) As the width of the multilayer insulating body is reduced, the capacitance generated between the signal line and the interlayer connecting conductor is increased, and the desired characteristic impedance as the transmission line is harder to realize.
(3) Because the interlayer connecting conductors have to be arranged between the signal lines, the width of the multilayer insulating body is inevitably increased.
For the reasons described above, the width of the transmission line is increased.